The royal pardon given to Michael Shields, the Liverpool football fan convicted of attacking a barman in Bulgaria, has been angrily condemned by a senior Bulgarian politician.

Shields, 22, from Liverpool, was pardoned by the justice secretary, Jack Straw, on Wednesday after a lengthy campaign.

Bar worker Martin Georgiev, a father of two, suffered a fractured skull when a paving stone was dropped on his head four years ago in the resort of Varna after Liverpool's Champions League victory.

Shields was jailed for 15 years by a Bulgarian court for attempted murder, which he denied. A campaign to free him was launched, supported by footballers and dignitaries including the Bishop of Liverpool, the Right Reverend James Jones. This week he became the first Briton convicted overseas to receive a royal pardon.

But Ivailo Kalfin, a Bulgarian former deputy prime minister, now an MEP, said he had been shocked by the decision, which was "giving a very bad signal to football hooliganism".

He said: "There were several people that were with Michael Shields in his group on that night. They had been drinking until the morning and they beat the bartender and threw stones on his head. This is a man who still has injuries and they will stay for life. There were a number of eyewitnesses."

He added that the case had been reviewed a number of times.

Another man, Graham Sankey, allegedly confessed to the attack when two of Shields's relatives visited his house on 22 July 2005, the second day of the trial. He subsequently withdrew his statement and now denies any involvement.

But Kalfin was dismissive of the Sankey evidence. "If there's somebody else who has admitted that they did it, then the next move is for them to appear in a Bulgarian court," he said.

Kalfin said he felt that in recent days "political considerations took over the need for justice". He said: "Jack Straw has to find some explanation for his decision but this is not convincing – several people saw the attack."

A Ministry of Justice spokesman disputed the MEP's claims of a political motive, saying: "Mr Straw took this decision alone based on advice from his legal team. He excluded political advisers."

Georgiev said: "I would be curious to know on what grounds they freed him. It's not for me to say, it was the court's decision. I am not the person who decides on the fate of Michael Shields. But I know that I am still in pain, my health is not good – a change in the seasons and I hurt more. Doctors were not sure that I would ever wake up, and if I did, they said, there was an 80% to 90% of not being normal and totally recovered."

Straw described Shields as "morally and technically innocent". He said: "I have now concluded, having looked at all the evidence … that Michael Shields is telling the truth when he says he is innocent."

Shields' legal team said it remained their intention to clear his name in court in Bulgaria. His barrister, Peter Weatherby, said: "We would hope the Bulgarian authorities would have regard to what Jack Straw has said and reopen the investigation."